Preservatives used in ophthalmic compositions are required to exhibit a sufficient antimicrobial effect on bacteria and fungi as well as a high degree of safety such that inducing no or small affection on eye tissues such as corneal epithelium. In addition to the original purposes as above, the preservatives themselves are required to be stable. Further, the preservatives are required to homogenize and stabilize the composition by interacting with the ingredients, for example, by homogeneously dispersing or dissolving the ingredients into the vehicle or base. Benzalkonium chloride is a preservative most commonly used in commercially available ophthalmic solutions.
However, preservatives are known as the major etiology of keratoconjunctive disorders, and for safety purpose, it is preferred that the concentration of a preservative such as benzalkonium chloride is below 0.01%. According to recent reports, preservatives contained in ophthalmic solution cause blood-aqueous barrier disruption and macular edema, especially cystoid macular edema (hereinafter referred to as “CME”) (The 105th General Assembly of Japan Ophthalmological Society, P. 112, OSN Supersite, Top Stories, 97/10/02, the contents are herein incorporated by reference).
Xalatan® ophthalmic solution, which has been marketed as a drug for treating ocular hypertension and glaucoma, contains latanoprost as an active ingredient thereof. Xalatan® ophthalmic solution contains benzalkonium chloride as a preservative at a concentration of 0.02% (package insert of Xalatan®), and side effects such as keratoconjunctive disorders and CME caused by such high concentration of the preservative have been the problem.
However, since latanoprost is highly fat-soluble, it has been believed to be difficult to prepare homogeneous and stable latanoprost ophthalmic composition without benzalkonium chloride. To the present, latanoprost ophthalmic composition containing no or less than 0.02% of benzalkonium chloride has not been provided as a commercially available product.